1973 Honda CB 350 carb re-build kits

I bought the bike new (in Canada) and have maintained it myself. The carbs are Keihin 722A - LB4 (left) and KKY (right). The Clymer service/repair handbook is not bad but the exploded view is not of the correct Carb. Also the carb float height height spec is wrong - should be 26 mm not 19. My main problem is getting a rebuild kit. Can anyone confirm the correct Keyster number is KH-1120? And, does anyone have experience with this carb? This or any Keyster product? Re-jetting (mine have 70 and 115 installed) ? Common problems? Suggestions? Is that little black nylon plug in the pilot jet hole really supposed to be there - blocking the fuel???
It runs well and has low mileage. Also has a new ignition system, cam chain, timing OK, etc... The only thing wrong with the performance is it has no power above 4000 to 6000 RPM (depending on the gear it's in)
I think it has to be carb trouble.
Thanks.

For anyone interested, I finally got the correct carb re-build kit for a 1973 Honda CB350G. It is a Keyster
KH-1200.
I had the carbs sonic cleaned, and with the re-build (with the correct parts) the bike now runs great!